12×20 Concrete Slab (4 inches): Yards, Feet & Bags
A 12 ft x 20 ft concrete slab is perfect for a patio or gazebo base. Assess your access for delivery and consider whether to use bags or ready-mix based on your project size and waste factor.
Choose Your Calculator
Slab Calculator
Enter any custom length, width, and thickness to get cubic yards and bag counts.
Open Slab CalculatorBag Calculator
Choose 40/60/80 lb bag sizes and estimate counts for your exact volume.
Open Bag CalculatorWant other sizes? Browse all slab size pages
Quick Answer
Tip: Always confirm the yield printed on your bag label. Bag yield guide
Large pour: consider ready-mix delivery for speed and consistent results. Bag counts this high can take significant mixing time.
Project Notes (Unique)
Always round to 0.25 yd³ when calculating your concrete needs and check yield on the label for accuracy.
Ensure your base is well-prepared and forms are secure, especially if you plan on thickened edges.
Finish the surface as desired and allow the slab to cure naturally for optimal strength and durability.
How to Estimate This Slab in 3 Steps
Measure
Length 12 ft, width 20 ft, thickness 4 in.
Compute Volume
Area: 240 sq ft → volume: 80.0 ft³ → 2.96 yd³.
Add Waste
Add a small buffer for spillage and uneven subgrade, then round up when ordering.
Planning Notes
Common uses: patio, gazebo base, walkway section.
For more context and conversions, see the Concrete Calculator hub.
Frequently Asked Questions
What should I consider when choosing between bags and ready-mix?
Consider your project size, access to the site, and whether you have the means to mix on-site.
How much extra material should I order?
It's wise to account for waste; a buffer ensures you have enough to complete the job without running short.
What is the best way to prepare the base for my slab?
Ensure the base is compacted and level, and consider using gravel for drainage and stability.
How thick should my concrete slab be for a patio?
A thickness of inches is generally sufficient for light to moderate use, providing a solid foundation.
Related Slab Sizes
Ready to Calculate Your Project?
Get instant estimates for cubic yards, cubic feet, and bag counts. No signup required.